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There is no need to guess. You can do dummy award bookings at aa.com and ba.com to see how many miles or Avios would be required for an award redemption down under. Keep in mind that BAEC is a distance-based scheme that charges for each flight flown; AAdvantage is a zone-based scheme that includes connecting flights for no extra charge. Note the special "wholly within one country" redemption rates on AA's Partner award chart (Australia and New Zealand count as a single country for purposes of that special redemption rate.)

Have you verified that the booking class of your QF U.S. to Australia flights qualifies for 100% earning in both the AAdvantage and BAEC programs? Some discounted Economy fares on QF only earn 25% of flown miles in AAdvantage and in BAEC.